1. Field of the Invention
The present invention relates to a fluororesin/ metal base functionally gradient material. More particularly, the present invention relates to a functionally gradient material comprising polytetrafluoroethylene and silver.
2. Description of the Related Art
As one of materials which can be used under severe conditions under which no single-component material can be employed, functionally gradient materials have been developed. The hitherto developed functionally gradient materials are based on the combinations of a metal and ceramics or ceramics and ceramics, but any functionally gradient material based on a polymer/metal combination has not been developed (cf. Masayuki Niino, "Generation of Functionally gradient Materials by the Application of Compositing Techniques", KOGYO-ZAIRYO, Vol. 35, No. 14, October 1987, 101-109).
As a material made of the polymer/metal combination, a polymer/metal composite material is known. However, not only the composite material has a homogeneous composition, but also the metal content has its own upper limit. This is because the object of compositing is to improve the properties of the polymer, that is, the compositing is intended to improve the specific properties of the polymer such as mechanical properties, thermal properties and electrical properties while maintaining the inherent properties of the polymer.
A temperature at which the polymer/metal composite material is molded is uniquely determined based on the type of polymer. At such a temperature, metal fillers are not bonded together or densified, and an increase in the amount of metal fillers would lead to a decrease in the mechanical strength or elongation of the composite material.
As the polymer/metal composite material in which the metal forms a matrix, a porous metal impregnated with a polymer is known. However, it is hardly possible to composite the metal and the polymer at an arbitrary ratio, because there will be many limitations placed on the composition range and microstructure thereof.
Accordingly, there has been neither polymer/metal functionally gradient material nor technique for widely varying the composition of the metal and the polymer within the composite material.
The polymer and the metal are in contact with each other in thermal, mechanical and electrical properties. For example, polytetrafluoroethylene and silver are compared. The coefficient of thermal conductivity is 0.2512 W/m.K for the former and 417.6 W/m.K for the latter. The Young's modulus is 5.13.times.10.sup.8 Pa for the former and 8.00.times.10.sup.10 Pa for the latter. The volume resistivity is 10.sup.18 ohm.cm for the former and 1.62.times.10.sup.-6 ohm.cm for the latter.
Therefore, it will be beneficial for the material design to drastically change the properties of the material by controlling the metal/polymer composition within a wide range.